from wikipedia...under baldness
Typically, Sex Hormone Binding Globulin or SHBG binds testosterone and controls the amount available in the blood. Lowered levels of SHBG result in more free testosterone, which can be converted into DHT by 5-alpha reductase.
Sex hormone binding globulin is reduced by high insulin levels. Thus, when insulin levels are high, free testosterone is increased. Most likely, increasing the level of free testosterone is one more way for our bodies to deal with high blood sugar. The level of free testosterone, and not total testosterone, is determinant of the level of DHT in the scalp. Thus, the level of DHT is directly linked to insulin levels.
Statistically, men who are bald are more likely to be insulin resistant and more likely to suffer cardiovascular disease. There seems to be a correlation between male pattern baldness and metabolic syndrome, though androgens are not shown to cause heart disease or metabolic syndrome\diabetes directly and actually may offer some protection against diabetes. High insulin levels seem the likely link between the two conditions.
Increased levels of Insulin Growth Factor-1 (IGF-1) has also been linked to vertex balding [3]
Increased incidence of androgenic alopecia has been linked to a high fat diet, the most notable example of which is the population of post WWII Japan, which saw its incidence of hair loss increase dramatically as it's intake of fatty foods also increased (and height increased as well.)
